Peripheral Nerve Stimulation for Chronic Pelvic Pain

Introduction

Over 16 million Americans between 18 and 50 years of age are impacted by chronic pelvic pain. This pain affects sexual intercourse, relationships, sleep, the ability to sit and walk, and work productivity, and is associated with depression, anxiety, and a significant impairment in quality of life. Chronic pelvic pain is often refractory to conservative medical management. When diagnostic peripheral nerve blocks prove beneficial, peripheral nerve stimulators may provide prolonged duration of analgesia. Today, based on similar technology initially used with sacral neuromodulation (e.g., Medtronic InterStim, Advanced Bionics ) to treat for nonobstructive urinary retention and overactive bladder syndrome, there are several percutaneous peripheral nerve stimulation (PNS) systems that have been used to successfully manage pain from peripheral neuropathies (e.g., Bioness StimRouter, SPR Therapeutics SPRINT, Stimwave ).

Anatomy

Chronic pelvic pain can occur in either sex and is defined as pain for at least 3 months between the iliac crest and the pelvic floor, including the inguinal and external urogenital area, and may include signs of central sensitization (e.g., hyperalgesia, referred pain, allodynia, decreased spinal reflex thresholds, enhanced summation of pain).

Visceral pelvic pain is typically characterized as dull, deep, sympathetically-mediated pain that may be secondary to stretch or inflammation of organs (e.g., urinary bladder, cervix, rectum, proximal anus, fallopian tubes, ovaries, prostate, testicles, uterus, upper four-fifths of the vagina). Visceral pelvic pain is conveyed via thoracic, lumbar, or sacral splanchnic nerves ( Table 36.1 ), and treatment with peripheral nerve stimulators is therefore ineffective.

Table 36.1

Sympathetically-Mediated Pelvic Visceral Innervation

Sympathetic Splanchnic Nerves That Innervate the Pelvis		Prevertebral/Paravertebral Ganglion/Plexus (Site of Synapse)	Innervation
Thoracic splanchnic (T5–T12)	Greater splanchnic (T5, T6, T7, T8, T9)	Celiac (receives innervation from aorticorenal plexus as well) Abdominal aortic plexus	Stomach, liver parenchyma, bile duct, pancreas, spleen, adrenal glands, small intestines, colon to splanchnic flexure
	Lesser splanchnic (T10, T11)	Aorticorenal Superior mesenteric Renal (also receives innervation from celiac ganglion) Ovarian/spermatic plexus Inferior mesenteric Superior hypogastric plexus	Descending colon, sigmoid colon, rectum, proximal anus, kidney, fallopian tubes, uterus, ovary, testicle, urinary bladder
	Least splanchnic (T12)
Lumbar splanchnic (L1, L2)		Fibers synapse at four lumbar ganglia, as well as abdominal aortic plexus, renal plexus, and inferior mesenteric ganglion
Sacral splanchnic (T12, L1, L2)		Fibers synapse at four to five sacral ganglia (including ganglion impar), as well as inferior hypogastric plexus (fibers ascend to superior hypogastric plexus, abdominal aortic plexus, and inferior mesenteric plexus)

On the other hand, somatic pain is described as sharp, localized, superficial pain that is caused by inflammation or trauma to skin (including external genitalia, distal one fifth of the vagina and distal anus), muscles, or bones. Somatic pain may be treated by targeting the nerves that innervate these regions (e.g., regional nerve blocks, peripheral nerve stimulators). Peripheral nerves that provide somatic innervation to the pelvis are listed in Table 36.2 .

Table 36.2

Somatic Pelvic Pain Innervation and Peripheral Nerve Stimulator Lead Placement Technique

Peripheral Nerve (Roots)	Nerve Course and Innervation Distribution	PNS Lead Placement Technique
Superior cluneal (T12, L1, L2, L3) ^a	Passes over the iliac crest through a thoracolumbar fascia and innervates iliac crest and upper buttock skin below the iliac crest	Patient prone. The incision is around L3, superior to the cluneal nerve. Insert the lead cephalad to caudad. Tunnel the remainder of the lead laterally to optimize patient comfort for pulse generator placement ( Fig. 36.1 ).
Ilioinguinal (L1+/1 T12) ^a	Leaves concavity of ilium to perforate the transverse abdominis muscle below the external oblique muscle at ASIS, may interconnect with iliohypogastric, and generally innervates the upper inner thigh, root of penis, upper scrotum, mons pubis, and lateral labia skin.	Patient supine. The incision is 1–2 cm inferomedial to ASIS. Lead inserted inferomedially towards the lateral aspect of the inguinal canal. Remainder of lead tunneled superior or medial depending on external stimulator placement. External stimulator sits on lateral lower abdomen ( Fig. 36.2 ).
Iliohypogastric (L1+/1 T12) ^a	Leaves concavity of ilium to perforate the transverse abdominis muscle below the external oblique muscle at ASIS, may interconnect with ilioinguinal, and generally innervates the lower lateral abdomen and inguinal region.	Patient supine. The incision is inferomedial to ASIS, approximately 7–10 cm superolateral from the nerve. Lead inserted inferomedially towards the genitals. Remainder of lead tunneled superolateral. External stimulator sits on lateral lower abdomen, out of the beltline ( Fig. 36.3 ).
Genitofemoral (L1,L2) ,	Passes through the psoas muscle. Divides into the (1) genital branch (goes through inguinal canal to innervate uterine round ligament, labia majora, and in males runs within the spermatic cord to innervate cremaster muscles and bottom of scrotum) and (2) femoral branch (passes beneath inguinal ligament to innervate a patch of skin on upper inner thigh).	Patient supine. The incision is inferomedial to ASIS, approximately 7–10 cm from the genitals. Lead inserted inferomedially towards the genitals. Remainder of lead tunneled superolaterally, depending on pulse generator placement ( Fig. 36.4 ).
Lateral femoral cutaneous (L2, L3) ^a	Leaves the psoas muscle, courses inferolaterally along iliacus, passes beneath inguinal ligament beneath fascia latae, and divides into anterior (anterolateral thigh) and posterior branch (lateral thigh).	Patient supine. The target area for lead placement is directly inferior to the junction of ASIS and inguinal ligament. The incision should be below the target. Tunnel remainder of lead lateral to the incision. Keep the external stimulator anterior to the iliotibial band.
Obturator (L2, L3, L4)	Leaves medial border of psoas muscle, travels via obturator canal to enter the thigh, divides into the (1) anterior branch (innervates hip joint, distal, medial thigh, and superficial hip adductor muscles) and (2) posterior branch (innervates deep hip adductor muscles and posterior knee joint).	Unlikely target due to depth of the nerve; however, an open technique in the operating room has been described.
Femoral (L2, L3, L4)	Descends laterally between psoas and iliacus muscles, enters iliac fossa, innervates iliacus muscles, passes beneath inguinal ligament in femoral sheath, innervates sartorius, quadriceps femoris, pectineus muscles, knee joint, anterior thigh, and medial calf skin.	This is an unlikely target for patients with chronic pelvic pain. Please see the chapter on femoral neuralgia Chapter 24 for technical details regarding lead insertion.
Sciatic (L4, L5, S1, S2, S3)	Travels inferiorly along anterior surface of piriformis muscle at sacrum, leaves pelvis inferior to piriformis muscle via sciatic notch, travels deep to obturator internus and gluteus maximus muscles, lies halfway between greater trochanter and the ischial tuberosity, continues posteromedial to femur, innervates hamstring and adductor magnus muscles, divides into the (1) tibial (innervates knee joint, majority of lower leg and foot muscles, posterior calf skin, and posterior, plantar, and lateral foot skin) and (2) common peroneal nerves (innervates knee joint, foot eversion muscles, and posterolateral upper calf and dorsolateral foot skin).	For chronic pelvic pain, a more likely target would be the pudendal nerve ( Chapter 22 ).
Superior gluteal (L4, L5, S1) ^b	Leaves pelvis through greater sciatic foramen above the piriformis by superior gluteal artery and vein and innervates gluteus medius, gluteus minimus, tensor fasciae latae, and piriformis muscles.	Unlikely target given the depth of the nerve, which would result in unreliable communication with the external stimulator.
Inferior gluteal (L5, S1, S2) ^b	Leaves pelvis via the greater sciatic foramen below the piriformis, innervates gluteus maximus muscle, and often communicates with the posterior femoral cutaneous nerve	Unlikely target given the depth of the nerve, which would result in unreliable communication with the external stimulator
Medial cluneal nerve (S1, S2, S3) ^a	Travels laterally deep or through long posterior sacroiliac ligament below PSIS to innervate the medial buttock skin.	Provides innervation to medial skin of the buttock; however, single lead placement at this nerve may not result in full coverage of the region. Lead placement is more likely at superior cluneal nerve ( Chapter 19 ).
Posterior femoral cutaneous (S1, S2, S3) ^a	Leaves pelvis through the greater sciatic foramen below the piriformis muscle, descends deep to gluteus maximus and fascia latae with inferior gluteal artery, pierces the deep fascia by small saphenous vein in middle posterior thigh, and branches to (1) inferior cluneal nerve* (innervates lower and lateral buttock skin), (2) perineal branch* (innervates upper, medial thigh skin), and (3) filaments that innervate posteromedial thigh and posterior upper leg skin.	This is an unlikely target due to its anatomic location.
Pudendal (S2, S3, S4)	Descends just proximal to the sacrospinous ligament, passes between the piriformis muscle and coccygeus muscle, leaves pelvis through lower part of greater sciatic foramen, crosses over lateral sacrospinous ligament, reenters pelvis through lesser sciatic foramen, travels anterocephalad adjacent to internal pudendal artery and vein along ischiorectal fossa lateral wall and through pudendal canal (obturator fascia sheath), divides to the (1) inferior rectal nerve (lower anal skin and external anal sphincter innervation), (2) peroneal nerve (perineum), (3) dorsal nerve of penis or clitoris (external genitalia skin and external urethral sphincter innervation).	Patient positioned in lateral decubitus with hips flexed and operative side up. The incision is superior and medial of the sciatic nerve. Lead is inserted in an inferolateral direction towards the pudendal nerve, lateral to the crossing of the sacrospinous and sacrotuberous ligaments, medial to the sciatic nerve and inferior to the piriformis. Lead is tunneled to superior medial aspect of the buttocks. The pudendal nerve runs alongside the pudendal artery, which may be visualized on ultrasound. Ideal lead placement is adjacent to the pudendal nerve and artery in the pudendal canal (Alcock’s canal) ( Fig. 36.5 ).

ASIS , Anterior superior iliac spine; PNS , peripheral nerve stimulation; PSIS , posterior superior iliac spine.

a Indicates a pure sensory nerve

b Indicates a pure motor nerve

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